Outlook Junk Folder Issues
Some people have reported an issue, where Outlook automatically sends emails to the "Junk" folder, without any rule (from the "Rules Wizard") to have it sent there. It is a good idea to set up a few rules to have certain types of email automatically sent to your Junk folder, (such as whenever the subject contains "Free", "Sale", etc.).
However, Outlook sometimes will suddenly begin sending important valued, trusted emails to the Junk folder !!
I do not have a sure-fire fix for this. But first make sure that you did not create a rule that unknown to you is causing havoc. You make your own set of rules for sending emails to the Junk folder, by using the Rules Wizard. This info is stored in a database file.
Actually, behind the scenes, Outlook does have it's own list of sender addresses that it will either block or move their emails to the Junk folder, or the Deleted Items folder.
Outlook 2000 - look for the file "Filters.txt" in \Program Files\Micorsoft Office\Office" - it will list the items that are auto-sent to the junk folder
Outlook 2003 - this recent version stores it's Junk filtering data in a file called "Outlfltr.dat". Microsoft has issued Outlook 2003 Junk E-mail Filter Update: December 16, 2003, the first update for Outlook 2003's junk mail filter. It replaces Outlfltr.dat to provide a more up-to-date definition of messages that are considered to be junk e-mail or not junk e-mail by the Outlook 2003 junk e-mail filter. For more information on what this file contains, see Outlook 2003's spam filter unmasked. (16 Dec 2003)